1. Field of the Invention
The present invention relates to a method of producing an electron emission device using an electron emission film, and a method of producing an image display device having a plurality of electron emission devices.
2. Description of the Related Art
Electron emission devices can be classified into three types: a field emission (FE) type, an MIM type, and a surface conduction type. Basically, in any type, the electron emission device includes a cathode electrode including an electron emission part and a control electrode for controlling emission of electrons from the electron emission part or controlling electrons emitted from the electron emission part.
Electron emission devices of the FE type can be further classified into two types: a type (Spindt type) in which an opening is formed in a control electrode and a cathode electrode made of metal and having a sharp tip (formed in a cone shape) is disposed in the opening, and a type in which a cathode electrode having a diamond thin film (electron emission film) having a rather flat shape is disposed in an opening of a control electrode. An example of a Spindt-type electron emission device is disclosed in Japanese Patent Publication No. 3094459. In recent years, an FE-type electron emission device has been proposed which uses a carbon fiber such as a carbon nanotube instead of a cone-shaped cathode electrode of a Spindt-type electron emission device. Examples of electron emission devices of the surface conduction type may be found in Japanese Patent Publication No. 3062987, Japanese Patent Laid-Open No. 2002-367508, Japanese Patent Laid-Open No. 8-162015, and Japanese Patent Laid-Open No. 2000-311596.
An example of an application of the electron emission device is a flat panel display composed of a large number of electron emission devices arranged on a single substrate. The flat panel display using electron emission devices is of emissive type (light emissive type), and thus it can display a high-quality image with a high brightness and high contrast even in a well-lit environment.
In recent years, there has arisen a need for flat panel displays capable of displaying an image with higher resolution. To this end, there is a need for an electron emission device capable of emitting electrons in the form of a small beam. In general, to reduce the beam diameter, it is effective to reduce the strength of the electric field which is formed when the electron emission device is driven (when electrons are emitted during its operation). Thus, there is a need for an electron emission device having an electron emission part capable of emitting electrons using low strength electric fields.
In flat panel displays, not only high brightness but also high-quality halftone (gray-scale image) representation is required. To achieve high-quality halftone representation, a large electron emission current and control of electron emission are required. To this end, it is desirable that the electron emission device has a clear threshold for electron emission. That is, it is desirable that the electron emission device does not emit any electron in electric fields lower than a threshold electric field Eth (or a threshold voltage Vth) and electron emission starts at the threshold electric field Eth. When such electron emission devices are used in a display, an off-state (a dark state) is obtained when the electric field is lower than Eth (Vth) and an on-state (bright state) is obtained when the electric field is higher than Eth (Vth). The contrast of the display is determined by the difference between the off-state (dark state) and the on-state (bright state). The higher the contrast, the better the halftone representation and the better the image quality.
It is also desirable that in the range of the electric field below Eth, no electrons be emitted and the current that has no contribution to the emission current (called a useless current or an ineffective current) should be as small as possible. That is, it is desirable that the electron emission device have as high an electron emission efficiency (=emission current/(emission current+useless current)) as possible. A high electron emission efficiency allows a reduction in power consumption and also a reduction in load imposed on a driver of the electron emission device.
It is also important that the electron emission device satisfying the above-described requirements can be produced with high repeatability and a high production yield.